Problems with an A-B VFD

[mtool]

I am running a fractional HP 3 phase motor with a Allen Bradley 1333 Variable Frequency AC drive. The motor will run at lower frequencies like 8-25hz, but as I raise the frequency the motor slows down and gets really weak. I've connected the motor directly to the line 3 phase power source and it works fine. Any suggestions?

 

[DickDV]

Lots of possibilities but I would first check to be sure the correct motor nameplate data has been entered into the drive parameters. Nothing works right until this is done.

 

[jraef]

I'd bet a dollar that you have the motor strapped for the wrong voltage, i.e. you have a 230/460V motor, you are using 230V but the motor is connected for 480V. At low speeds the loss of torque is not as noticeable because you are doing less work and maybe you have the Torque Boost feature enabled, which boosts the voltage at low speed (this was NOT a vector drive remember). Torque boost goes away as you increase the output speed, so the extreme loss of torque at that point is not even enough to continue on with acceleration.

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[lectricwes]

This wouldn't happen to be used as a phase converter; i.e. single phase to three phase?